Container for nuclear fuel transportation

ABSTRACT

A transport container for nuclear fuel is provided with an outer container having internal insulation, the insulation defining an internal cavity. The cavity receives a plurality of fuel containers wherein the internal volume of the fuel containers is at least 5% of the external volume of the outer container. The container allows substantially higher volume proportions of enriched fuel to be safely transported than is possible with prior containers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/969,835, filed Oct. 21, 2004, which is a continuation of patentapplication Ser. No. 10/618,833, filed Jul. 14, 2003, U.S. Pat. No.6,825,483, which is a continuation of patent application Ser. No.10/022,993, filed Dec. 18, 2001, U.S. Pat. No. 6,770,897, which is acontinuation of patent application Ser. No. 09/829,677, filed Apr. 10,2001 (abandoned), which is a continuation of patent application Ser. No.09/180,029, filed May 7, 1999 (abandoned), which is a U.S.nationalization of International Application No. PCT/GB97/01197, filedMay 2, 1997, which claims priority to Great Britain Application No.9609304.2, filed May 3, 1996, which applications are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

This invention concerns improvements in and relating to fueltransportation, particularly but not exclusively relating to enrichednuclear fuels.

2. The Relevant Technology

Nuclear fuels, such as enriched uranium or mixed oxide forms, frequentlyneed to be transported between sites, for instance the enrichment siteand the fuel rod production site. The fuel is normally in the form ofpellets or powder at this stage. International standards apply,requiring certain levels of thermal insulation and structural strength.A major concern is criticality control. The mass of enriched fuel withinthe transport container must be strictly limited to ensure that acriticality event does not occur. This single requirement places astringent limit on the volume of fuel which can be transported in anygiven volume of a transport container. In this regard, thetransportation of nuclear fuel differs significantly from transportationof other radioactive materials. Radioactive waste is of a far lowerenrichment, thus facilitating transport of greater volumes in proximitywith one another. In assembled fuel rods on the other hand, the volumeof fuel when compared with the overall fuel rod and supporting structurevolume is very low.

SUMMARY OF THE INVENTION

Present systems usually consist of a cylindrical drum provided with oneor more layers of wood on all sides, the wood defining a central recessinto which a single cylinder containing the enriched fuel is placed.

The fuel containing volume of the inner drum is very low compared withthe volume of the outer drum. As a consequence the transportation offuel takes up a considerable amount of space. The commercialconsiderations of this apply as they do to any transportation procedure.Additionally the cylindrical nature of the unit presents handling andstability problems.

According to a first aspect of the invention we provide a transportablecontainer for nuclear fuel, the container comprising an outer containerprovided with internal insulation, the insulation defining an internalcavity, the cavity receiving a plurality of fuel containers, wherein theinternal volume of the fuel containers is at least 5% of the externalvolume of the outer container.

A container having this level of fuel volume to overall volume has notpreviously been achieved. The present invention also allows this levelto be reached whilst meeting the necessary criticality, insulation andother standards.

Preferably the internal volume of the fuel container is at least 10% ofthat of the external volume of the outer container. A level of at least15%, 20% or 25% is preferred. Levels of at least 30%, 35% or even 40%may be reached. Any increase in fuel volume to overall container volumeis significant in reducing transportation costs and the capital costsinvolved in providing the strong fuel containers.

Preferably the outer container is formed with a steel and mostpreferably stainless steel skin. The corners and/or edges of the outercontainer may be provided with strengthening elements. These may takethe form of L-shaped sections. The outer container is preferablyprovided with feet.

The outer container is preferably provided with a lid. The lid ispreferably releasably fastened to the outer container. Clamps attachedto the outer container and releasably engageable with the periphery ofthe lid are preferred. The clamps may also be releasably engaged withthe outer container. The lid may be provided with handles or other formsof engagement for removal of the lid.

It is particularly preferred that the lid be received within theperimeter of two or more projections from the outer container. Thestrengthening elements projecting above the top of the container maydefine this perimeter.

Preferably the insulating material is provided in a series of discretelayers. One or more base layers and/or one or more wall layers for eachwall may be provided. The lid insulation may be mounted on the metal lidor may be provided separately. If provided separately a pair ofinterlinking sections may be provided.

The insulating layer is preferably thermally insulating and/or neutronabsorbing. Calcium silicate offers a preferred insulating material. Oneor more different materials may be used together or in a sandwich stylestructure.

Preferably the insulation layer defines the boundaries of a singleinternal cavity. A rectilinear cavity is preferred.

The internal cavity is preferably provided with a correspondingly shapedsingle unit internal container comprising four side walls and a base.The internal container is preferably made of steel, boronated steel, ormost particularly stainless steel.

In one form the internal container is preferably divided up into aseries of chambers. The chambers may be defined by one or more elementscrossing the internal cavity or container. Preferably the elements areplates spanning the full height, or at least substantially the fullheight, of the internal volume. Preferably one or more elements span theinternal volume in different directions, most preferably atsubstantially 90 degrees to one another. Preferably the plates aresubstantially vertically provided. It is particularly preferred that twoplates cross the internal cavity in each of two directions at 90 degreesto one another. Preferably the internal volume is divided up into ninesubstantially equivalent chambers.

In a second alternative form, the internal cavity may be fitted withelements such as plates spanning the full height of the internal volumeto define an internal container. The chambers again being defined by oneor more elements crossing the internal cavity. A base plate may beprovided on the base insulating layer to define a base for the internalvolume. A top plate may also be provided. Side plates may also beprovided to define the sides of the chambers.

One or more of the base, top or dividing elements or plates may beformed of metal. Steel and in particular stainless steel or boronatedsteel.

The base, side and dividing plates or elements of the single unitinternal container are alternatively provided as a separate unit to theinsulating layers and outer container.

In a further alternative form the internal cavity may be fitted with aplurality of sleeve elements. Preferably the sleeve elements are adaptedto receive fuel containers or pails. The sleeves may be continuous orsubstantially continuous. Preferably the sleeves are of circularcross-section. Preferably the sleeves' internal diameter issubstantially equivalent to the external diameter of the fuel containersor pails. Preferably the sleeves are rigidly separated from one another.The sleeves may be rigidly separated by mounting on a base plate.

Preferably the sleeves are discrete from one another around their entireperiphery. Four or more, and preferably 8 or 9 such sleeves may beprovided within the internal cavity.

The base plate may be attached to one or more side plates or elements.The side plates or elements may form walls corresponding to the walls ofthe internal cavity. An internal container may thus be provided.

Preferably one or more of the sleeves are at least in part surrounded bya neutron absorbing material. Preferably one or more of the sleeves, andmost preferably all of the sleeves, are surrounded by a neutronabsorbing material around their entire circumference. A neutronabsorbing material may optionally be provided around one or both ends ofone or more of the sleeves.

Preferably the neutron absorbing material is a resin based material.Preferably the neutron absorbing material is fire resistant. Preferablythe resin based material is loaded with, up to 6.5% boron, or up to 5%boron, and more preferably up to 2.5% boron. Preferably the resinoccupies at least 50% of the non-sleeve volume of the internal cavity.The neutron absorbing material may fill the entire non-sleeve volume ofthe internal cavity or lower density materials may be incorporated, suchas polystyrene.

The internal container is preferably provided with a lid.

Preferably the fuel containers or pails comprise cylindrical drums.Preferably releasable lids are provided. The release mechanism for thelid is preferably contained within the plan profile of the container inthe sealed position to minimize space.

The fuel preferably occupies at least 50% of the fuel container and mayoccupy 60, 70, 80, 90, 95% or any individual % value over 50%.

The fuel may be provided within the fuel containers in plastic bags,such as polyethylene.

The fuel may be in pellet, powder or other form. Unirradiated enricheduranium may be the fuel. The provision of uranium at substantially up to5% enrichment may be used. A density of around 1.4 g/cm³ may be used. Insuch a case each individual fuel container may have a volume of between15 and 20 liters, for instance 17.3 liters.

The boron content of any one of the insulator layers, internaldivisions, sleeves, fuel containers, or remaining chamber space may beincreased to give increased absorption.

Fuel containers are preferably provided in more than three of thechambers or sleeves. The provision of the fuel containers in peripheralchambers or sleeves and most preferably all the peripheral chambers orsleeves is envisaged. One or more of the chambers or sleeves may beprovided with a neutron absorber. Preferably the neutron absorber isprovided in a unit corresponding in dimensions to the chamber or sleevereceiving it. The provision of polyethylene as the neutron absorber ispreferred. The polyethylene absorber may be in a steel containercorresponding to the size and shape of the chamber or sleeve receivingit. The absorber may also be provided with a lid corresponding with thechamber or sleeve into which the absorber is placed in order to assistin retaining the absorber within the chamber or sleeve. The lid ispreferably of steel.

In a particularly preferred form the container comprises an outercontainer with a removable lid, the outer container being provided withan insulating layer on each wall and base, a further removableinsulating layer being provided between the lid and the internal cavityof the container in use, the internal cavity being divided into aplurality of chambers, a fuel container being provided in at least threeof the chambers and at least one of the chambers being provided with aneutron absorbing material.

In an alternative particularly preferred form the container comprises anouter container with removable lid, the outer container being providedwith an insulating layer on each wall and the base, a further removableinsulating layer being provided on the lid, the insulating layersdefining an internal cavity of the container, the internal cavity beingprovided with a plurality of sleeves, a fuel container being provided inat least 3 of the sleeves and the sleeves being at least partiallysurrounded by a neutron absorbing material.

It is preferred that only one fuel container or pail be provided in eachchamber.

A particularly preferred arrangement provides a rectangular planaperture divided into nine chambers, three chambers by three chambers.Preferably the fuel containers are provided in the peripheral chambers.A neutron absorbing material may be substituted in the central chamberand/or one or more of the other chambers as required.

In a further particularly preferred arrangement a rectilinear planinternal cavity may be provided with nine sleeve elements, in a three bythree sleeve element arrangement. Preferably fuel containers areprovided in all the periphery sleeves and most preferably in all of thesleeves. A neutron absorbing material may be substituted in one or moreof the chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will now be illustrated, by way ofexample only, and with reference to the accompanying drawings in which:—

FIG. 1 shows a perspective view of a container according to a firstembodiment of the invention cut away to show the fuel containers in thecontainer;

FIG. 2 shows a cross-sectional side view of FIG. 1;

FIG. 3 shows a pail load in plan view;

FIG. 4 shows a side view of the container of FIG. 1;

FIG. 5 shows a plan view of a closed container according to the firstembodiment of the invention partly cut away to show the fuel containersin the container of the invention;

FIG. 6 shows one embodiment of a fuel container or pail for use in thepresent invention's outer container;

FIG. 6A shows a plan view of a fuel container or pail of FIG. 6;

FIG. 7 shows a perspective view of the container according to a secondembodiment of the invention, cut away to show the fuel containers in thecontainer;

FIG. 8 shows a pail load in plan view; and

FIG. 9 shows a cross-sectional side view along axis XX of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The container as illustrated in FIG. 1 has the general form of arectangular box. The container 1 is defined by four vertically arrangedwalls 2 and a base wall 3. The walls are provided at the corner jointswith strengthening elements 4 in the form of L-shaped strips. Thevertical strengthening elements 4 have portions 6 which extend beyondthe lid 8 of the container. Feet 10 are provided on each corner of thebase and engage with the portion 6 for easy and stable stacking.

The outer skin forming the walls 2, base 3 and separate lid 8 are madeof stainless steel.

A peripheral flange 12 is provided around the container. The lid 8 isdimensioned to be slidably received within the boundaries of theL-shaped elements 4. The lid 8 has a flange 16 which corresponds withthe peripheral flange 12 of the container. Handles 14 on the lid aid inits removal and insertion.

In the closed and retained position shown the lid 8 is retained by aseries of quick release nuts and bolts 18 which engage correspondingopenings in the flange 16 of the lid 8. The lid is provided withsuitable seals to prevent any ingress of water.

Next to the steel skin the container is provided with a substantialthickness of a thermal insulator 20 formed from calcium silicate. Thislayer is provided in a series of sections, see FIG. 2. The materialsprovision in solid sections ensures accurate positioning during assemblyand use. A single base layer of insulator 22 and four wall sections 24line the container itself. When the container is loaded, as describedbelow, a two piece insulating top layer is applied. These two pieces 26,28 are shaped to interconnect with one another.

The rectangular box defined by the interior surfaces of the insulatinglayers receives an internal container 30A having four walls and a baseand also made of boronated steel or stainless steel. This container 30Ais also provided with a lid 31 as shown in FIG. 1. As seen in FIG. 3 thecontainer consists of a series of interlocking vertical walls 30 made ofboronated steel/stainless steel. The container 30A has two pairs ofinternal walls 30 at 90 degrees to one another defining nine chambers 32within the pail load.

In use within each of the eight peripheral chambers a fuel drum or pail36 is received. The central chamber 32A is provided with a polyethyleneneutron absorber 38. The absorber 38 is itself provided in a steelcontainer (not shown) which corresponds with the shape of the chamber 32into which it is to be fitted. A lid is provided on the top of theabsorber to retain the absorber in place in the chamber 32A.

Once the internal container 30A has received all eight fuel drums 36,the container 1 is sealed by applying the lid 31, the insulating toplayer 26, 28, and the external lid 8. The lid 8 is secured to thecontainer 1 by the quick release nuts and bolts 18.

The fuel containing drum 36, as illustrated in FIG. 6, consists of astainless steel cylinder wall 40 with a base plate 42 and releasable lid44. The lid 44 is provided with a standard internal lever clamp band 46which enables the lid to be secured to the fuel drum 36. The provisionof the internal lever clamp band 46 within the outline of the drum 36 isimportant to minimize the space taken up. In the closed state the drum36 is water tight avoiding any water ingress.

The fuel 55 in either powder or pellet form is contained withinpolyethylene bags. The polyethylene bags filled with fuel are placed ina larger polyethylene bag which is placed in the drum. Once the largerbag is full it is then closed. The drum is then sealed with the lid 44.The fuel may typically be enriched uranium destined to form fuel rods.

In the second embodiment of the invention illustrated in FIG. 7 thecontainer 100 is once again in the form of a rectangular box. Theexternal container 100 is defined in a similar manner to the containerof the first embodiment by vertically arranged side walls 102 and a basewall 103. Other equivalent elements are numbered with reference numeralscorresponding to those used in the first embodiment increased by 100.

Thus the strengthening elements, feet, peripheral flange, lid fixing andlid alignment are provided in a similar manner.

The container 100 is also provided with substantial thickness of thermalinsulator 120 provided by a base section, wall sections and a sectionoptionally mounted on the lid in a similar manner to the firstembodiment of the invention.

The arrangement within the internal cavity defined by these insulatinglayers differs, however.

The cavity is provided with a series of stainless steel sleeves 150which are rigidly mounted on a bottom plate standing on the base layerinsulation. The cylindrical sleeves are hollow and have an internaldimension configured to snugly correspond to the external dimensions ofthe fuel containers 152 shown inserted in the sleeves 150. Nine sleeves150 are used in a three by three arrangement with a fuel container 152being positioned in each in use.

The fuel containers are generally of the type illustrated in FIG. 6 and6A above, but include external fasteners projecting beyond the plan ofthe fuel containers.

As shown in FIGS. 7, 8 and 9 the sleeves 150 are surrounded by a neutronabsorbing material 158. This material is introduced to the volumesurrounding the sleeves during the manufacture of the portion of theassembly filling the internal cavity by pouring in a liquid resin whichis then allowed to harden. A resin tight unit is preferred as definingthis cavity. The resin is loaded with boron preferably to a level of 2%to provide the desired neutron absorbing capability. A boron loading upto 6.5 wt % and/or a lead loading up to 15 wt % may be provided. Thematerial offers between 1×10²² and 1×10²³ hydrogen atoms/cm³

To reduce the cost and weight of the neutron absorbing material,typically 1.68 g/cm³ or lighter materials such as polystyrene can beincorporated in portions where the neutron absorbing volume of materialwould otherwise be excessive. Thus at locations 162 between sets of 4sleeves and externally at the corner locations 164 and locations 166between the pairs of sleeves the neutron material may be replaced withthe lighter material. This does not affect the neutron absorbingcapability of the container.

The fuel containing drums 152 and the manner in which the fuel, aspowder or pellets is provided within them is as described above for thefirst embodiment of the invention.

The present invention allows approximately 20%-40% of the outercontainer volume to be occupied by fuel 55 and yet still meets thenecessary standards. This compares favorably with prior art systems. Anincreased payload is thus provided successfully.

The use of stainless steel and the modular nature of the assemblyassists in refurbishment and any cleaning stages required such asdecontamination.

1. A transportable container for nuclear fuel comprising: an outercontainer bounding an interior and defining an overall volume; a thermalinsulation material disposed within the interior bounded by the outercontainer, the thermal insulation material bounding an internal cavity;a plurality of sleeves disposed within the cavity; and one or more fuelcontainers received within at least one of the sleeves, each of the oneor more fuel containers having an internal volume and a releasable lid.2. A container according to claim 1 in which the sleeves are surroundedby a neutron absorbing material, the neutron absorbing material fillingthe internal cavity apart from the inside of the sleeves.
 3. A containeraccording to claim 1 in which the volume of the internal cavity outsideof the sleeves is filled by neutron absorbing material or neutronabsorbing material which incorporates lower density materials.
 4. Acontainer according to claim 1 in which the sleeves are rigidlyseparated from one another.
 5. A container according to claim I in whichthe outer container is comprised of steel, the sleeves are comprised ofstainless steel and have a substantially circular transversecross-section, the sleeves having an internal diameter that issubstantially equal to an external diameter of the fuel containers, thesleeves being rigidly separated from one another, the sleeves beingsurrounded around their entire circumference by a neutron absorbingmaterial, the fuel containers being comprised of stainless steel havinga substantially cylindrical configuration, and nuclear fuel beingdisposed within the fuel containers in plastic bags.
 6. A containeraccording to claim 1 in which the outer container is provided with alid.
 7. A container according to claim 1 in which only one fuelcontainer is provided in each sleeve.
 8. A transportable container fornuclear fuel comprising: an outer container bounding an interior anddefining an overall volume; a thermal insulation material disposedwithin the interior bounded by the outer container, the thermalinsulation material comprising one or more base layers and one or morewall layers; and a plurality of chambers being provided within boundsdefined by the thermal insulation material, one or more fuel containersbeing provided within each of a plurality of the chambers.
 9. Acontainer according to claim 8 in which the chambers are surrounded by aneutron absorbing material, the neutron absorbing material filling thebounds defined by the insulation apart from the inside of the chambers.10. A container according to claim 8 in which neutron absorbing materialor neutron absorbing material which incorporates lower density materialsfills the volume around the sleeves.
 11. A container according to claim8 in which the internal bounds of the thermal insulation materialcontact a neutron absorbing material.
 12. A container according to claim8 in which the internal insulation is neutron absorbing.
 13. A containeraccording to claim 12 in which the interior bounds of the neutronabsorbing insulation contact a neutron absorbing material.
 14. Acontainer according to claim 12 in which the neutron absorbing materialis loaded with boron.
 15. A container according to claim 8 in which theouter container is comprised of steel, the sleeves are comprised ofstainless steel and have a substantially circular transversecross-section, the sleeves having an internal diameter that issubstantially equal to an external diameter of the fuel containers, thesleeves being rigidly separated from one another, the sleeves beingsurrounded around their entire circumference by a neutron absorbingmaterial, the fuel containers being comprised of stainless steel havinga substantially cylindrical configuration, and nuclear fuel beingdisposed within the fuel containers in plastic bags.
 16. A transportablecontainer for nuclear fuel, the container comprising: an outercontainer, the outer container being provided with a thermal insulationmaterial disposed therein; a plurality of laterally spaced apart sleevesprovided within the outer container; and one or more fuel containersreceived within the one or more of the sleeves, the fuel containers eachbeing provided with a releasable lid for the fuel container.
 17. Acontainer according to claim 16 in which the releasable lid for the fuelcontainer seals the fuel container when fastened and the releasable lidfor the outer container seals the outer container when fastened.
 18. Acontainer according to claim 16 in which the outer container and outercontainer lid provides a first barrier and the fuel container and fuelcontainer lid provides a second barrier between the nuclear fuel and theexterior of the outer container.